The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
In a motor vehicle transmission, closed throttle downshifts can be thought of as an inverted power-on upshift. During such situations, if a lift-out of torque (i.e. a reduction in torque), typical clutch control strategies detect lift-out conditions and modify the control strategy to address the rapidly decreasing torque. The same condition can occur during negative torque regenerative braking closed throttle downshifts when the driver removes pressure from the brake (i.e. brake lift-out) during the clutch control process. Specifically, in particular hybrid arrangements, the coast regenerative torque can vary through the shift process depending on the driver brake input and a desire to maintain constant power to the wheels of the motor vehicle. While braking at high regenerative levels, when the driver lifts out of the brake, it is expected that the level of deceleration returns to a normal level. Thus the torque must be ramped out a predetermined level. Current clutch control strategies, however, are unable to handle situations in which the torque changes rapidly. In particular, current clutch control strategies cannot predict and control the proper clutch pressure to torque relationship.
Accordingly, there is a need for an improved clutch control strategy during brake lift-out.